Pressure receptacle and closure therefor



Feb. 24, 1953 J. OTTMAR ETAL PRESSURE RECEPTACLE AND CLOSURE THEREFOR 2SHEETS-SHEET 1 Filed Feb. 6, 1948 FIGS.

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7 x I m u H N a W Feb. 24, 1953 J. OTTMAR ET AL 2,629,513

PRESSURE RECEPTACLE AND CLOSURE THEREFOR Filed Feb. 6, 1948 2SHEETSSHEET 2 49 39 11 9 a 5 /53 e'3 1? 59 a1 Patented Feb. 24, 1953UNITED STATES PATENT OFFICE PRESSURE RECEPTACLE CLOSURE THEREFORApplication'l ebruary 6, 1948, Seria1-No. 6,'684

(Cl- .Z.

'15 Claims. 1

This invention relates to pressure receptacles and closures therefor,and more particularly: to pressure cookers and like vessels andtoremovable lids or covers for tightly sealing such vessels to holdpressure therein.

Among the several objects of the invention may be noted the provision ofa pressure receptacle such as a pressure cooker or like vessel having'an improved, readily removable closure comprising acover or lid adaptedtightly to seal the receptacle sothat pressure may build up therein; theprovision of a receptacle. and closure therefor or" the class Idescribed wherein the closure comprises'a cover or lid which seatsexternally upon the vessel so "as to be readily removable, yet which isadapted increasingly to'seal the receptacle as" the pressure within thereceptacle increases; theprovisionof a receptacle and closureconstruction of this class which enables the receptacle to beformed'without any obstructions that would interfere with the pouring ofthe contents of the receptacle; the provision of a closure of the classdescribed adapted automatically to vent the receptacle until itscontents are heated to a predetermined temperature to permit air toescape, and then automatically to seal the receptacle for pressurecooking-or the like; and the provision of a closure such asdes-cr'ibedwhich is easy to apply and remove so that it is particularlysuitable for usewitha household pressure cooker, Other objects will bein-par-t apparent and in part pointed out hereinafter.

The invention accordinglyccmprises the elements and combinations of,elements; features of construction, and arrangements of parts which willbe exemplified in the structures hereinafter described, and the scope ofthe application of which will be indicatedin the following claims.

In the accompanyingdrawings, in which one of various possibleembodiments of the invention is illustrated,

Fig. l is a side elevation of a pressure receptacle and closureembodying this invention;

Fig. 2 is an end view. of the receptacle and closure, as viewedfrom theright of'Fi-g. 1;

Fig; 3 is a plan view of the receptacle and closure;

Fig. 4 is a horizontal section taken on line 4-4 of Fig. 6, but ,on asmaller scale than the latter;

Fig. 5 is an enlarged vertical section, taken on line 5-5 of Fig. 3;and,

Fig. 6 is a view similar to Fig: 5; but showing parts in adifferentoperating position.

' Similar reference characters--indicate correspending parts-throughout:the several views of the drawings.

Referringtto the drawingsa pressure cooker orlike pressurereceptacleofthis invention is shown-generally to .comprise a vessel orv cooker :bodyManda removable. .closure3. The vessel I has a cylindrical wall; 5 and abottom I, being open .at its upper-end. -I t isprovided withan externalflange a9 -at.-its.mouth, andwith an up wardly facing .conicaLseatingsurface ll surrounding its-mouth .for peripheral sealing engagement by.a novel cover or lid, generally designated [3. The vessel is alsoprovided with an external flange 15 spaced. from flanges to form anexternal annular; groove H. The interior of the vessel is unlessotherwise desired wholly smoothand unobstructed so that there is nointerferenceto pouringv of its contents over any portion of the.sloping, annular seating surface H.

The closure 3 includes .a bridgemember is carrying the lid I3 andadapted detachably to be locked to the vessel 1 in position above andspanningitssmouth, with .the lid in position to close the vessel.,Asillustrated, the bridge memb er i9 is; in egrally formed at one endwith a dependin book 2 I engageablein the annular groove l1. Anotherhook,23; is pivoted in the bridge member to dependtherefrom adjacent itsother end as indicated at; 25. The latter hook is adapted. .to .;swinginto and out of the annular .groove l1;diamet rically o posite hook 2|for detachably lockingqtheubridge memberjil and lid iscarriedflthereby.toqthe. vessel. ,A portion of the bridge memberextending outward beyond the pivot 25 forms a handle 27. Means forlatching the pivoted hook 23 in. engagement in annular groove. H isillustratedas comprising a'latch .29 threaded ,in a longitudinal .bore3! in the handle. 1Theinner. endof the rod 29 is. adapted to engageinanotch 33,-inthe-upper end of hook 23 to prevent pivotal movementthereofupon its engagement in annular groove .i'L- The outer. end :oithe rod 29 is providedwith aknob 35ior conveniently threading it into orout of the notch or otherwise centrally upon its upper face. The latteris threaded into the boss, as indicated at 45. The peripheral portion ofthe plate M is bent downward to form a depending annular rim 41, so thatthe plate is of inverted dish or saucer shape. This annular rimfunctions as a fulcrum member in cooperation with lid IS in a manner tobe described.

The lid [3 comprises a circular resilient plate, preferably a dished,snap-acting plate of thermostat bimetal formed in accordance with thedisclosure in the Spencer United States Patent 1,448,240 to have twooppositely bowed positions of stability dependent upon its temperature,these positions being illustrated in Figs. 5 and 6, respectively. Thelid is preferably provided with a peripheral sealing ring 49 of rubberor other suitable material, adapted to seal upon the seat H of thevessel in the Fig. 6 position of the lid. It is carried by the bridgemember l9 substantially concentric with the seat in such manner that itmay snap between its Figs. 5 and 6 positions. The lid I3 is mounted withits high-expansion component 5| towards the outside and its lowexpansioncomponent 53 towards the inside of the vessel. Thus, it occupies theposition of Fig. 5 when its temperature is below a predetermined value.In this cold position it is bowed away from the vessel, being convexwith respect to the vessel, and ring 49 is spaced outward from seat I I,completely free from sealing engagement with the seat, to vent thevessel. The lid I3 occupies the position of Fig. 6 when its temperatureis above a predetermined value. In this hot position it is bowed towardthe vessel, concave with respect thereto, and ring 49 seals upon theseat II. The lid engages and reacts against the rim or fulcrum 41 ofplate 41 in either of its positions. The terms convex and concave relateto the inside surface of the plate 41 as viewed from a point within thevessel.

The rubber ring 49 may be fastened in any suitable manner upon theperiphery of the lid 13. As herein illustrated, the ring is providedwith an internal groove 54 receiving the periphery of the plate. Thering when untensioned is of somewhat smaller diameter than lid l3, andthus is retained upon the lid stretched under tension when applied. Thisconstruction permits ready removal and replacement of the sealing ring.

The lid i3 is centrally supported from the plate 41 by means permittingvertical movement of its central portion relative to the plate. As illustrated, this means comprises a vent pipe 55 which extends through acentral aperture 51 in the lid I3. The latter is tightly retained (toprovide against inadvertent leakage) upon the lower end of the vent pipebetween collars 59 and BI provided on the pipe. If necessary, a sealinggasket (not shown) can be used in conjunction with collars 59 and BI.The upper collar 59 ma be formed integrally with the pipe and the lowercollar may be riveted upon a reduced-diameter portion at the lower endof the pipe, as illustrated at 63.

The vent pipe extends upward from the lid I9 freely through a centralapertur 65 in plate 4! into the chamber formed by recess 3'! and boss39, where it is externally threaded. A nut 61 is threaded on the upperend of the pipe above the plate 4! to retain the pipe in assembledrelation with the plate and to provide for adjustment of the lid I3 toregulate the temperature at which it snaps from its cold position ofFig. 5 to its hot position of Fig. 6. This adjustment is made by turningthe nut to vary the vertical distance from the center of plate 41 to thecenter of the lid when the latter is in its cold position of Fig. 5. Tolower the temperature at which the lid will snap from its cold to itshot position, the nut is threaded down on the pipe thereby to draw upthe center of the lid closer to the plate 4!. To raise this temperature,the nut is threaded up on the pipe to relieve the restraint upon thelid. The collar 59 and the nut 5'! limit the movement of the center ofthe plate.

The nut 61 is looked in adjusted position by means of a lock nut 69threaded on the upper end of the vent pipe. The lock nut is in the formof a cap having an aperture H in its upper end in communication withtehe vent pipe. The lock nut provides a valve seat for a pressure reliefvalve comprising a valve member or stem 73 loosely slida'ble verticallyin an aperture T5 in the bridge member 59, and biased downward by aweight TI on the upper end of the stem. The lower end of the valve stem13 is tapered to enter the aperture ll in the upper end of the lock nut.Stem 13 is suihciently loose in aperture 75 for steam venting purposes.

When the lid [3 is in its vessel-sealing position of Fig. 6, it issubjected to stress and deformation by the force due to pressure withinthe vessel acting upon the central circular portion of the lidcircumscribed by the rim 41, by the force due to pressure within thevessel acting upon the annular peripheral portion of the lid outward ofthe rim, and by the inherent internal force within the lid due to itsthermostatic action under heat. The force due to internal pressureacting upon the central circular portion of the lid circumscribed by therim 41 establishes a moment about the rim which tends to bulge thisportion of the lid upward and outward, thus tending to cause the lid toflex concavely with respect to the vessel. The force due to internalpressure acting upon the annular peripheral portion of the lid outwardof the rim 4! establishes an oppositely directed moment about the rimwhich tends to cause this portion of the lid to flex upward about therim, thus tending to cause the lid to flex convexly with respect to thevessel. The inherent internal force within the lid due to itsthermostatic action tends to cause the lid to flex concavely. All theseforces are resisted by the rim, which functions as a fulcrum about whichthe lid may flex.

To attain a seal, the rim 4! is made of such diameter that the combineddefor-mative action of the effective moment of the force due to internalpressure acting upward upon the central circular portion of the lidcircumscribed by the rim and the inherent thermostatic action of thelid, both of which tend to cause the lid to flex concavely, is greaterthan the deformative action of the effective moment of the force due tointernal pressure acting upward upon the annular peripheral portion ofthe lid outward of the rim. The result is that the upward bulging of thecentral circular portion of the lid (the area bounded by the line A,Figs. 3 and 4) and the downward flexing of the lid due to thermostaticaction overcome the tendency of the annular peripheral portion of thelid (the area outside line A) to bend upward. The latter portionconsequently flexes downward about the rim 41 as a fulcrum, thus forcingthe peripheral sealing ring 49 of the lid into sealing engagement withthe seat II. As the pressure within the vessel and the temperatureincrease, the "seal becomes tighter. i a I V The diameter of the rim 4'!may be such that the effective moment of the total force due to internalpressure acting upon the central circular portion of the lid within lineA tending to bulge it upward and outward is either greater than, equalto, or somewhat less than the effective moment of the total force actingupon the annular portion of the lid outside line A tending to unseat thesealing ring 49. It is preferable that the rim it! be of such diameterthat the effective moment of the total force due to internal pressureacting upon the central circular portion of the lid is greater than theeffective moment of the total force due to internal pressure acting uponthe annular peripheral portion 'of, the rim, in which case sealingaction is attained irrespective of the thermostatic action of the lid.This, however, is not essential because a sealing action will beattained even if these opposing moments are equal because of thethermostatic action of the lid. Assuming that the diameter of the rim llis such that the opposing moments due to internal pressure are equal andcancel out, it will be apparent that, when the lid is heated and hassnapped to its closed position of Fig. 6, heat will cause the lid totend to become more concave with respect to the vessel. This is becausethe high expansion component 5! of the lid is on the outside and the lowexpansion component 53 is on the inside. Once thelid has snapped,continued heating causes the marginal portion of the lid to tend tocreep further in the direction of the seat H. This is an inherentcharact'eristic of snap-acting plates of the type used herein. The rirnll takes the reaction caused by the creeping action of the lid, and atight seal is attained.

Furthermore, the diameter of the rim 4! may even be such that theeffective moment of the total force acting upon the central circularportion of the lid is somewhat less than the effective moment of thetotal force acting upon the annular peripheral portion of the lid andstill attain a sealing action, as long as the thermostatic action of thelid is sufficient to overcome the difference of the moments. Under thesecircumstances, if the difference of the moments acting upon the annularperipheral portion of the lid outward of the rim should become greatenough to overcome the thermostatic action of the lid, the peripheralportion of the lid will bend upward to vent the vessel. This will occurat a predetermined increase in pressure. By properly designing the lidas to its thermostatic action, mechanical strength, and location of thefulcrum rim il, it is possible to make thelid self-opening for ventingpurposes in response to increase in pressure inthe vessel above apredetermined safe value. That is, the lid may be designedto remainsealed by its inherent thermostatic action up to a predetermined, safeinternal pressure, and to open to vent the vessel at that pressure dueto the pressure overcoming the thermostatic action of the lid. i

In a practical embodiment of this invention wherein the diameter of rimiii (of thermostat metal having a flexivity of 145 l0 by AmericanSociety of Testing Materials standards) is approximately 6% inches, wehave found that the diameter of rim 4'! (line A) may be varied fromapproximately 4% inches to 4% inches with a tight sealingactionthroughout this range, using metal .040 inch thick.

6 Operationi's a's renews: I i Assuming this invention to be embodied"in 'a pressure cooker, the 'food to be cooked is placed in the vessel 1"and'a sufiic'ientquantity of water'to generate steam is added,-ifrequired. The closure 3 is'applied by engaging hook 2| in the annulargroove 1 "i with hook 23 loose, then looking the closure to the vesselby engaging hook 23 in the groove and latching it by means of latch rod29.

The lid :3 'is'now cold and occupies the upwardlybowed, openposition ofFig.5, wherein the sealing ring 49 is substantially spaced from the seatl i so that the vessel'is freely vented'to the atmosphere.

Upon heating the vessel, steam is generated and forces air from thevesel. The lid i3 is heated by the steam, byradiation, conductionandcondensation, to its hot snapping temperature, whereupon it"sna'p'stoits downwardly bowed position of Fig. 6, wherein the-sealing ring 49seals against the seat H. The loose connection of the vent pipe in theplate 4| permits upward movement of the *cente'r'of 'the'lid as itsnaps. The weight Ti maintains valve member '13 seated to close the ventpipe so that pressure builds up in the vesel. If the pressure'shouldbecome excessive, however, the valve member 53 is unseated against thebias-of the weight l! to vent the vessel through the vent pipe until thepressure is reduced to a safe value.

As the allowable pressure builds up in the vessel, it forces the lid l3against the rim d1 of the plate iii. The pressure causes the centralportion of the lid within the rim to bulge upward. The annular portionof the lid outside the rim is forced downward about the rimas a fulcrum,thus forcing the sealing ring 49 into increasingly tighter sealingengagement with the seat H as the pressure and temperature increase.This results from the unbalanced forces acting upon the lid in themanner above described. Movement of the center of the lid is permittedby the loose connection of the vent pipe in the plate 4|.

When cooking is completed, the vessel is cooled until the lid i3 snapsfrom its Fig. 6 to its Fig. 5 position. This vents the vessel, relievingany residual vacuum therein, so that the entire 010- sure 3 maybereadily removed.

While the lid I3 has been particularly illustrated as a dished,snap-acting plate of thermostatic bimetal so as automaticaly to vent thevessel when its temperature is below a predetermined value, it will beapparent that the lid may be a non-thermostatic dished plate, or even aninitially fiat plate, where automatic venting action is not essential.While such a lid will not provide for automatic venting action, it willprovide for increasingly efiective sealing of the vessel with increasein internal steam pressure. It will be understood that where the lid isnon-thermostatic the diameter of rim t? must be such that the moment ofthe force of the steam acting on the central portion of the lid isgreater than the moment of the force of the steam acting'on the annularperipheral portion of theiid, since such a lid does nothave anythermostatic action. This relationship of the moments is most readilyattained by making the rim of such diameter as to bound an inner areawhich is greater than the'area outward of the rim so that the totalforce acting on the central portion of the lidis greater than the totalforce acting on the annular peripheral portion of the lid. p i H W I, H

In view of the 'above'lt will testes thatthe several objects of theinvention are achieved and other advantageous results attained.

As many changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

We claim:

1. A pressure receptacle comprising a vessel having an exterior seatsurrounding its mouth, a lid for the vessel comprising a dished,snapacting thermostatic plate, means on the ve se centrally supportingthe plate at and concentric with the mouth of the vessel, the peripheryof the plate being freely movable with respect to the vessel so that theplate can snap between a first position wherein it is bowed away fromthe vessel and out of sealing engagement with said seat and a secondposition wherein it is bowed toward the vessel with its periphery insealing engagement with said seat, and a generally annular fulcrummounted upon the vessel in engagement with the exterior of the plate andsubstantially concentric therewith.

A pressure receptacle comprising a vessel having an exterior seatsurrounding its mouth, a lid for the vessel comprising a dished,snapacting thermostatic plate, means on the vessel centrally supportingthe plate at and concentric with the mouth of the vessel, the peripheryof the plate being freely movable with respect to the vessel so that theplate can snap between a first position wherein it is bowed away fromthe vessel with its periphery out of sealing engagement with said seatand a second position wherein it is bowed toward the vessel with itsperiphery in sealing engagement with said seat, and a generally annularfulcrum mounted upon the vessel in engagement with the exterior of theplate at points so spaced from its center that the combined deiormativeaction of the effective moment of the total force due to internalpressure acting upon the portion of the plate circumscribed by thefulcrum and the inherent thermostatic action of the plate is greaterthan the deformative action of the effective moment of the total forcedue to internal pressure acting upon the portion of the plate outward ofthe fulcrum.

3. A pressure receptacle comprising a vessel having an exterior seatsurrounding its mouth, a lid for the vessel comprising a dished,snapacting thermostatic plate, means on the vessel centrally supportingthe plate at and concentric with the mouth of the vessel, the peripheryof the plate being freely movable with respect to the vessel so that theplate can snap between a first position wherein it is bowed away fromthe vessel with its periphery spaced from and out of sealing engagementwith said seat and a second position wherein it is bowed toward thevessel with its periphery in sealing engagement with said seat, and agenerally annular fulcrum mounted upon said vessel in engagement withthe exterior of said plate at points so spaced from its center that theeffective moment of the total force due to internal pressure acting uponthe portion of the plate circumscribed by the fulcrum is greater thanthe effective moment of the total force due to internal pressure actingupon the portion of the plate outward of the fulcrum.

4. A pressure receptacle comprising a vessel having an exterior seatsurrounding its mouth, a lid for the vessel comprising a dished,snap-acting thermostatic plate, means on the vessel centrally supportingthe plate at and concentric with the mouth of-the vessel, the peripheryof the plate being freely movable with respect to the vessel so that theplate can snap between a first position wherein it is bowed away fromthe vessel with its periphery spaced from and out of sealing engagementwith said seat and a second position wherein it is bowed toward thevessel with its periphery in sealing engagement with said seat, and agenerally annular fulcrum mounted upon the vessel in engagement with theexterior of the plate at points so spaced from its center that theeffective moment of the total force due to internal pressure acting uponthe portion of the plate circumscribed by the fulcrum is substantiallyequal to the effective moment of the total force due to internalpressure acting upon the portion of the plate outward of the fulcrum.

5. A pressure cooker or the like comprising a vessel having an exteriorseat surrounding its mouth, a lid for the vessel comprising a dished,snap-acting thermostatic plate, means on the vessel centrally supportingthe plate at and concentric with the mouth of the vessel, the peripheryof the plate being freely movable with respect to the vessel so that theplate can snap from a normal cold position wherein it is bowed away fromthe vessel out of sealing engagement with said seat to vent the vesselto an oppositely bowed position with its periphery in sealing engagementwith said seat, and a generally annular fulcrum mounted upon the vesselin engagement with the exterior of the plate at points so spaced fromits center that at a predetermined pressure within the vessel theeffective moment of the total force due to internal pressure acting uponthe portion of the plate outward of the fulcrum overcomes thethermostatic action of the plate and the effective moment of the totalforce due to internal pressure acting upon the portion of the platecircumscribed by the fulcrum to vent the vessel.

6. A pressure receptacle comprising a vessel having an exterior seatsurrounding its mouth, a

lid-carrying member detachably connected to the vessel, a lid for thevessel comprising a dished, snap-acting thermostatic plate carried atits center by said member concentric with the mouth of the vessel andwith its periphery free of said member and the vessel so that it cansnap between a first position wherein it is bowed away from the vesselwith its periphery spaced from and out of sealing engagement with saidseat and a second position wherein it is bowed toward the vessel withits periphery in sealing engagement with said seat, and a generallyannular fulcrum carried by said member bearing against the exterior ofthe plate at points so spaced from its center that the combineddeformative action of the effective moment of the total force due tointernal pressure acting upon the portion of the plate circumscribed bythe fulcrum and the inherent thermostatic action of the plate is greaterthan the deformative action of the effective moment of the total forcedue to internal pressure acting upon the portion of the plate outward ofthe fulcrum.

"I. A pressure receptacle comprising a vessel having an exterior seatsurrounding its mouth, a bridge member detachably mounted on the vesselin position spanning its mouth, a lid comprising a dished, snap-actingthermostatic plate carried at its center by said bridge member concentric with the mouth of the vessel and with its periphery free of saidmember and the vessel so that it can snap between a first positionwherein it is bowed away from the vessel out of sealing engagement withsaid seat and a second position wherein it is bowed toward the vesselwith its periphery in sealing engagement with said seat, the center ofthe plate being movable relatively to the bridge member, and a generallyannular fulcrum on the bridge member bearing against the exterior of theplate on a line bounding an inner plate area so related to the platearea out side the line that the effective moment of the total force dueto internal pressure acting upon the area bounded by the line is greaterthan the effective moment of the total force due to internal pressureacting upon the area outside the line.

8. A pressure cooker or the like comprising a vessel having an exteriorseat surrounding its mouth, a lid for the vessel comprising a dished,snap-acting thermostatic plate, means on the vessel centrally supportingthe plate at and concentric with the mouth of the vessel, the peripheryof the plate being freely movable with respect to the vessel so that theplate can snap from a normal cold position wherein it is bowed away fromthe vessel with its periphery spaced from and out of sealing engagementwith said seat to vent the vessel to an oppositely bowed position withits periphery in sealing engagement with said seat, and a generallyannular fulcrum mounted upon the vessel in engagement with the exteriorof the plate at points so spaced from its center that the combineddeformative action of the eifective moment or the total force due tointernal pressure acting upon the portion of the plate circumscribed bythe fulcrum and the inherent thermo static action of the plate isgreater than the deformative action of the effective moment of the totalforce due to internal pressure acting upon the portion of the plateoutward of the fulcrum.

9. A closure for pressure receptacles comprising a bridge member adaptedto span the mouth of a receptacle, means on the bridge member fordetachably looking it to a receptacle in position spanning its mouth, alid for the receptacle comprising a resilient plate supported from thebridge member by means permitting movement of the central portion of theplate relative to the bridge member, and a generally annular fulcrum onthe bridge member bearing against the outer face of the plate at pointsso spaced from the center of the plate that the combined deformativeaction of the eifective moment of the total force due to pressure actingupon the inner face of the portion of the plate circumscribed by thefulcrum is greater than the deformative action of the effective momentof total force due to pressure acting upon the inner face of the portionof the plate outward of the fulcrum.

10. A closure for pressure cookers and like vessels comprising a bridgemember adapted to span the mouth of a vessel, means on the bridge memberfor detachably locking it to a vessel in position spanning its mouth, alid for the vessel comprising a dished, snap-acting thermostatic platecentrally supported from the bridge memher by a loose connectionpermitting movement of the central portion of the plate relative to thebridge member, and a generally annular fulcrum on the bridge memberbearing against the outer face of the plate on a line bounding an innerplate area so related to the plate area outward of the line that theeffective moment of the total force due to internal pressure acting uponthe area bounded by the line is greater than the effective moment of thetotal force due to internal pressure acting upon the area outside theline.

11. A closure as set forth in claim 10 wherein said connection isadjustable to vary the snapping temperature of the plate.

12. A closure as set forth in claim 10 wherein said connection includesa vent pipe extending through the plate, and a pressure relief valvecarried by the bridge member for controlling flow through said ventpipe.

13. A closure as set forth in claim 10, wherein said plate has aperipheral sealing ring for sealing the mouth of the vessel.

14. A closure as set forth in claim 10, wherein said plate has a ring ofrubber or the like fitted upon and stretched around its periphery.

15. A pressure receptacle comprising a vessel having an exterior seatsurrounding its mouth, a bridge member detachably mounted on the vesselin position spanning its mouth, said bridge member being provided with acentral plate having a depending annular rim substantially concentricwith said seat, a resilient lid peripherally engageable with said seatand having a central vent pipe extending upward loose- 1y through acentral aperture in the plate, means on the pipe above the plate holdingthe lid assembled with the bridge member and in position for engagementwith the annular rim, said means being spaced from the lid a distancesuch that the center of the lid may move within limits relative to theplate, and a pressure relief valve associated with the upper end of thepipe.

JEROME OTTMAR. GEORGE A. MATTE'SON, JR. UNTO U. SAVOLAINEN. PAUL G.CHACE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 526,785 Lewis Oct. 2, 1894:1,106,837 Pfaehler Aug. 11, 1914 1,109,828 Golf Sept. 8, 1914 1,834,837Hashimoto Dec. 1, 1931 2,309,617 Benson Jan. 26, 1943 2,387,380 SmithOct. 23, 1945 2,426,800 Triplett Sept. 2, 1947 2,447,493 Daniel Aug. 24,1948 2,516,202 Graham July 25, 1950

